1. Field of the Invention
The present invention relates to a spindle motor and a disk drive apparatus.
2. Description of the Related Art
Spindle motors arranged to rotate disks are typically installed in hard disk apparatuses and optical disk apparatuses. Such a spindle motor includes a stationary portion fixed to a housing of the apparatus, and a rotating portion arranged to rotate while supporting the disk(s). The spindle motor is arranged to produce a torque by magnetic flux generated between a stator and a magnet, whereby the rotating portion is caused to rotate with respect to the stationary portion.
The stationary portion and the rotating portion of the spindle motor are joined to each other through a fluid dynamic bearing. A known spindle motor including a fluid dynamic bearing is described, for example, in US 2012/0033329. The spindle motor described in US 2012/0033329 includes a bearing mechanism including a lubricant oil (see paragraph [0047] and FIG. 3 of US 2012/0033329).
In the spindle motor as described above, once a lubricant oil vaporizes through a liquid surface of the lubricant oil, a gas including the lubricant oil is caused by a centrifugal force to flow radially outward along a surface of the rotating portion. Once the gas flows radially outward along the surface of the rotating portion, a component of the lubricant oil included in the gas may be adhered to a surface of a disk to cause an error in reading or writing of information from or to the disk.
The spindle motor described in US 2012/0033329 includes an annular axially extending gap having a locally decreased radial width between a radially inner edge of a seal cap and an inner cylindrical surface of an upper thrust portion (see paragraph [0077] and FIG. 8 of US 2012/0033329). This structure reduces the likelihood that the gas including the lubricant oil vaporized through the liquid surface of the lubricant oil will leak out of the bearing mechanism.
However, a further improvement in storage density of the disk requires that the reading and the writing of information from or to the disk should be performed with higher precision. This in turn makes it necessary to prevent a gas including even a little lubricant oil which has leaked out of the bearing mechanism from being adhered to the disk.